A multichamber type processing device adopting the so-called cluster structure is employed in the process of manufacturing semiconductor devices, LCD substrates and the like in the related art. A multichamber type processing device normally includes a vacuum transfer chamber, a plurality of vacuum processing chambers provided around the vacuum transfer chamber and a vacuum cassette chamber. In this structure, workpieces housed inside a cassette placed within the vacuum cassette chamber are sequentially transferred into the individual vacuum processing chambers by a transfer arm provided in the vacuum transfer chamber to allow various types of processing such as etching to be implemented continuously. In addition, the atmosphere within the vacuum transfer chamber in the processing device is sustained at a reduced pressure. This makes it possible to first deliver the cassette from the atmosphere side into the vacuum cassette chamber, reduce the atmosphere inside the vacuum cassette chamber to a level substantially equal to the level of the pressure inside the vacuum transfer chamber and then transfer the workpieces from the cassette into the vacuum transfer chamber.
Now, the structure assumed in a standard vacuum cassette chamber 10 that may be provided in the processing device described above is explained in reference to FIG. 4. As illustrated in the figure, a cassette stage 16 on which a cassette 12 is set is supported by a drive shaft 14 in the vacuum cassette chamber 10, and the stage 16 is driven to move up/down and rotate freely by a drive mechanism (not shown). By adopting this structure, it is possible to adjust the orientation of the cassette 12 on the stage 16 as necessary and to move workpieces 24 set over multiple stages within the cassette 12 up and down to adjust their heights to the position at which they are transferred to the transfer arm (not shown).
The drive mechanism that drives the elevator shaft 14 is provided outside the vacuum cassette chamber 10. Thus, the drive shaft 14 passes through a through hole 19 formed at a vacuum container 18 enclosing the vacuum cassette chamber 10 and connects the drive mechanism and the stage 16. Between the drive shaft 14 and the inner wall of the through hole 19, a slight gap is formed to ensure that the vertical motion and the rotational motion of the drive shaft 14 are not hindered, and an O-ring 20 is provided at this gap. The O-ring 20, constituted of an elastic material, is provided in complete contact with the drive shaft 14 and the inner wall of the through hole 19, and thus, the gap between the drive shaft 14 and the inner wall of the through hole 19 is sealed without hindering the vertical or rotational motion of the drive shaft 14. This structure ensures that the presence of the drive shaft 14 extending through the vacuum cassette chamber 10 and outside of the vacuum cassette chamber 10 does not compromise the airtightness of the vacuum cassette chamber 10. In addition, a lubricant 22 is applied onto the contact surface where the drive shaft 14 and the O-ring 20 achieve contact with each other, thereby reducing the force caused by the friction between the drive shaft 14 and the O-ring 20.
However, there is a problem in that if a large area of the drive shaft 14 is exposed into the vacuum cassette chamber 10, the lubricant 22 applied onto the surface of the drive shaft 14 may cause contamination of the workpieces 24. In addition, the lubricant 22 becomes worn faster as the vacuum cassette chamber 10 is evacuated, resulting in an increase in the frictional force between the drive shaft 14 and the O-ring 20.
An object of the present invention, which has been completed by addressing the problems of the related art discussed above, is to provide a new and improved vacuum processing device capable of solving the problems discussed above and other problems as well.